1. Field of the Invention
This invention relates to an apparatus for forming a film, suitable for forming a monomolecular film, or a monomolecular layer-built-up film, i.e. a laminate of monomolecular layers, which will be hereinafter referred to as "LB film", and particularly to an apparatus for forming a film, which is distinguished in forming films having various built-up structures, where different monomolecular layers are laid one upon another.
2. Description of the Prior Art
Heretofore, inorganic materials with relatively easy handling characteristics have been mostly utilized in the fields of semi-conductor technique and optical technique, partly because the technical progress in the field of organic materials was considerably retarded, as compared with that in the field of inorganic materials.
However, the recent rapid technical progress in the field of organic materials is quite remarkable and also it is often said that the development of inorganic materials is approaching their limit. Thus, development and research for novel organic functional materials that can surpass the inorganic functional materials are now keenly desired.
Organic materials enjoy such advantages as low cost, easy production, high functionality, etc. Though the organic materials have been so far regarded as poor materials in heat resistance and mechanical strength, novel organic materials, which have overcome these disadvantages, have been recently made available one after another. Under such recent technical situations, it has been proposed by some research organizations to make some or all of the parts, mainly film parts, which play the function of a logic element, a memory element, photoelectric converter element, etc. as in integrated circuit devices, or the function of a microlens array, an optical waveguide, etc. as in optical devices, from an organic film in place of the conventional inorganic film, as well as to make a molecular electron device in which one organic molecule is made to play the function of a logic element, a memory element, etc., or even to make logic elements from bio-related substances, for example, bio-chips.
The organic film as the main constituent for such devices can be prepared according to a monomolecular layer building up technique. The monomolecular layer building up technique, which may be also called "Langmuir-Blodgett's technique" or "LB technique", is a method comprising regularly spreading molecules each having a hydrophilic group and a hydrophobic group on water by utilizing the hydrophilic and hydrophobic properties of the molecules, thereby forming a monomolecular film thereon, and then transferring the monomolecular film onto the surface of a substrate, where it is possible to form a monomolecular film or a monomolecular layer built-up film, i.e., a laminate of monomolecular layers, on the substrate.
The conventional apparatus for forming such a film has a structure as shown in FIG. 6. That is, a frame 2 is provided within a shallow, broad rectangular water vat 1 to partition the water surface 3. The frame 2 works as a two-dimensional cylinder, and a rectangular float 4 is provided on the water surface within the frame 2. The width of float 4 is a little smaller than the inner width of frame 2 and the float 4 can be smoothly moved horizontally, that is, toward the left or right side on the drawing, as a two-dimensional piston. To move the float 4 horizontally, the float 4 is connected to a winder 6 driven, for example, by a motor, or the like, through a wire 5.
To form a monomolecular film, a monomolecular film-forming substance is dissolved in a volatile solvent such as benzene, chloroform, etc., and a drop of the resulting solution is added to the water surface 3. After evaporation of the solvent, a monomolecular film showing a two-dimensional behavior remains on the water surface 3. When the surface density of the molecules is low, the film is called a two-dimensional gaseous film. By moving the float 4 toward the right side, the extension of the water surface 3 on which the monomolecules are spread is contracted to increase the surface density. Thus, the intermolecular action is so intensified that the gaseous film is changed to a two-dimensional solid film through the intermediate stage of a two-dimensional liquid film. In the solid film, the arrangement and orientation of the molecules become regular and uniform, and the high orderliness and uniform ultra-thin filminess required for the semi-conductor constituent materials can be obtained.
To transfer the monomolecular film from the water surface 3 onto the surface of substrate 7, a vertical dipping technique is used, where the substrate 7 fixed to a substrate holder 8 is moved in a vertical direction 9, while applying a suitable constant surface pressure for the building-up operation to the monomolecular film on the water surface 3, thereby transferring the monomolecular film onto the substrate 7. The technique includes 3 types, i.e., type X, in which a monomolecular film 10 is deposited onto the substrate 7, only when the substrate 7 is dipped, as shown in FIG. 7(a); type Y, in which the monomolecular film 10 is deposited onto the substrate 7, also when the substrate is pulled up, as shown in FIG. 7(b); and type Z, in which the monomolecular film 10 is deposited onto the substrate 7, only when the substrate is pulled up, as shown in FIG. 7(c). In FIG. 7, numeral 11 shows the hydrophilic moiety of the molecule, whereas numeral 12 shows the hydrophobic moiety of the molecule.
When, for example, a built-up film shown in FIG. 2 is to be formed as a type Y heterogeneous monomolecular layers-built-up film, which is a laminate of different monomolecular layers laid one upon another in the building-up direction [see FIG. 7(b)], that is, when hetero junctions are to be provided between the hydrophilic groups 11a of film A and the hydrophilic groups 11b of film B, the substrate is moved vertically and reciprocally to deposit films A.sub.1 and A.sub.2, and, then, while the substrate is made to stay dipped in the water, the monomocular film A on the water surface is discarded to clean the water surface. Then, a monomolecular film B is formed on the cleaned water surface, and the substrate is again moved vertically and reciprocally to deposit films B.sub.1 and B.sub.2. Further film A can be likewise deposited.
For the monomolecular film exchange, on the water surface, said apparatus will require much time in cleaning the water surface, and much more time as one increases the number of different monomolecular films. Furthermore, the water surface may be rippled or the water level may fluctuate at the cleaning of the water surface for the monomolecular film exchange, with the result, that the film formed on such water surface cannot be uniformly deposited onto the substrate and thus cannot be used for the building-up.
As described above, the conventional apparatus requires much time and labor in forming a built-up film, i.e., a laminate of different monomolecular layers on a substrate, and has the disadvantage of unavoidably requiring the discarding of the useful monomolecular film as waste.